Name: Water Resources
Uploaded: 2020-02-08T06:52:45.000Z
Duration: 11 min 38 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Hi. It's Mr. Andersen and this is environmental science video 5. It is on water resources.

Basic passive voice

Our body is filled with over 60 percent water. And this does not seem like a big deal because

the earth is covered with over 70 percent water. The problem with that is that most

of that is sea water that we cannot use. And the freshwater that remains, most of it is

going to be frozen in ice caps and glaciers. And so the percent that is really fresh water

on the surface is a small percent of the water on our planet and it is finite. The amount

of water we have on our planet has never changed. Now as the sun provides energy to the earth

the water will move around through the hydrologic or the water cycle but we have a finite amount

of water. And most of it is going to be sea water. We have a little bit of fresh water.

The sea water moves around through ocean currents. The fresh water could be divided into ground

water, water underneath the surface and then surface water which is on the surface. Now

we need that water. We need it domestically in the home to take a shower or to drink.

But we also need it in industry to make our goods. And most of it actually goes to agriculture

to make the food that we eat. The problem with water on our planet is that it is unevenly

distributed. In some areas there is lots of water. In some areas however there is going

to be scarcity. And so humans have had to learn how to store water, move it around and

in the future we may have to desalinate some of that sea water so that we can use it as

fresh water. Now where is that ground water stored? It is underneath the ground in aquifers

that we can deplete. What about the surface water? Well it can be stored in reservoirs

that occur naturally or ones that are created as we produce dams. And then we can move it

around through aqueducts and even to the planet itself through irrigation. But we have a finite

amount and so conservation is incredibly important. And economics have contributed to water loss

and could help us to actually solve this water conservation problem. And so the hydrologic

cycle works like this. Anywhere there is water on the surface we can have evaporation. That

gets cooled and eventually leads to condensation and precipitation. Once it is on the surface

we call that surface water. It is running over the surface. That could be lakes and

swamps and rivers. After we have that water hit the ground it can however be infiltrated

into the soil and the ground itself. To give you an example of that imagine I have a beaker

here. Is it full? Well maybe full of air. If I put marbles in it, is it full? No you

can see there is spaces in it. What if I fill it up with sand? Is it full? No. There is

still spaces in there. If I fill it up with water now we are starting to fill up that

beaker. And that is what infiltration is. As the water flows down into the soil we call

that now ground water. Let's say it is not filling that whole beaker. It is right here.

That point at which we have saturation in the ground water is called the water table.

Most of our planet is covered with water, unfortunately it is seawater. It has salt

dissolved in it. If you drink it you will die. If we put it on our fields the crops

are going to die. Now it moves around using currents. We talked about that in the last

video on the atmosphere, it is cells in the atmosphere and coriolis effect. So we have

these general trends in circulation. But also salinity affects it. And so if we look at

an area right here it is a high salt concentration because we have a lot of evaporation. But

up here we have a lot of melting of that glacial ice. And so we are going to have a low salt

concentration. And so the salt concentration and differences in heat create these thermohaline

circulations that really make that whole ocean on our planet one system. Now if we look at

fresh water it can be divided into water that is above the surface, we call that surface

water and then ground water. But what is interesting is if we look to the sides of that stream

you can see the water table in the ground water. And so if you dig a hole right here

it is just going to fill in with water because of all of that ground water around it. Now

this is an aquifer. It is storage of that water in the ground water. We call this unconfined

aquifer because the water can move between the surface and the aquifer itself. If I were

to dig down a little bit we could find what is called a confined aquifer. And that is

going to be stuck between this impermeable rock down here and above it. Now let's say

we want to get to that ground water on the surface. If we want some of the surface water

we simply pump it out of the stream. But if we want to get water out of that ground water

we could dig a well. Now the water, we could either pump out the water or sometimes we

will have what is called an artisan well where there is either enough gravity above it or

enough pressure in the ground water so it actually comes out. But as we use that well,

just like using a stream the water table is going to drop. And so we are going to start

to deplete that aquifer. Now an important term in filling an aquifer is something called

recharge. So as we get water and infiltration we are going to fill up that aquifer. But

if the outputs, in other words if we pull out more water then we are putting in, we

are going to deplete the aquifer. And what are we using all of this fresh water for?

Well if we break it out using a pie chart most of it is actually for agriculture. The

growing of our food. We use some of it for industry. And then some of it domestically

in the house. The problem again is that it is unevenly distributed on our planet. Brazil

is going to have plenty of water. But if we look in the desert southwest of the US or

in the Sahara there is not going to be any water right there. And so what have humans

done? We have started to store water. So reservoirs are an example of that. A big example would

be the Three Gorges Dam that was built in China. It was finished in 2006. And so this

is what that river, the Yangtze River looked like before they built the dam. And then they

built the dam, finished in 2006. You can see what it looks like then. So we are storing

the water behind the dam. What is nice about that, now we have water that we can use at

will. We also can get energy from it, as we run that water through a generator. We can

control flooding downstream. And also we can use that for irrigation. Or the Three Gorges

Dam they are using to increase shipping on the Yangtze River. So it sounds great. What

is the problem? Well there is going to be destruction wherever that water went. So we

are decreasing 20 percent of the forest in this Yangtze River. We are displacing over

1,000,000 people that used live there. We also have evaporation of the water off the

surface. And then we are going to have nutrients that start to deposit there that would have

normally moved their way down the river. And that is going to disrupt wildlife. And so

fish obviously cannot spawn, move up and down in the stream. But it is also going to change

the temperature of the water. An example. There is a freshwater dolphin that went extinct

in the Yangtze River and the Three Gorges Dam may have contributed to that. We can also

store it underground. That is naturally stored in what are called aquifers. One of the largest

ones on the planet is the Oglala Aquifer. It is going to be found in the midwest. And

so here it is in Nebraska. But it goes all the way down to Texas and up into South Dakota.

It is a huge aquifer. So if we look at the amount of water stored underground it is over

1000 feet of infiltrated saturated water underneath the ground that we can use. And you can see

right here that there is tons of irrigation going on. This is in Kansas. They are using

center pivot irrigation so they can grow their crops. It seems great but what happens again

is that we can deplete that. So if we look at, this is during a 15 year period of time,

there is an increase in the aquifer in certain areas but most of the time we are seeing depletion.

And sometimes that aquifer has kind of disappeared. And a lot of scientists think in the next

100 years the Oglala Aquifer is just going to disappear. Why is that a problem? It could

take another 6000 years to fill it up again through natural recharge. Now we also have

to move water around. So looking to California is a great example of that. So if we look

in California they need a lot of water in the central valley and then in the south,

Los Angeles and San Diego. So they built this huge system where they can move water where

it is, in the mountains, and they can move it through these aqueducts to where it is

needed. Now you can see that is controversial. So people in this area are saying you are

depleting our rivers. In this area we are saying we have more population. We are growing

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Water Resources

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